Optical recording medium and method for recording data in the same

Abstract

An optical recording medium includes a substrate, two recording layers provided on the substrate and two dielectric layers each provided adjacent to one of the recording layers, the optical recording medium being constituted so that when it is irradiated with a laser beam having a wavelength lambda via an objective lens having a numerical aperture NA satisfying lambda / NA<=640 nm from the side opposite from the substrate, a record mark whose reflection coefficient is different from those of other regions of the recording layers is formed in the recording layers and at least a part of a region(s) of the dielectric layers adjacent to the record mark is crystallized to form a crystallized region. According to the thus constituted optical recording medium, it is possible to reproduce a signal having excellent signal characteristics.

Description

[0001] The present invention relates to an optical recording medium and a method for recording data in the optical recording medium and, particularly, to an optical recording medium capable of reproducing a signal having excellent signal characteristics and a method for recording data in the same so that a signal having excellent signal characteristics can be reproduced.DESCRIPTION OF THE PRIOR ART[0002] Optical recording media such as the CD, DVD and the like have been widely used as recording media for recording digital data. These optical recording media can be roughly classified into optical recording media such as the CD-ROM and the DVD-ROM that do not enable writing and rewriting of data (ROM type optical recording media), optical recording media such as the CD-R and DVD-R that enable writing but not rewriting of data (write-once type optical recording media), and optical recording media such as the CD-RW and DVD-RW that enable rewriting of data (data rewritable type optical r...

AI Technical Summary

Benefits of technology

[0012] It is another object of the present invention to provide a method for recording data in an optical recording medium so that a signal having excellent signal characteristics can be reproduced.

[0013] The inventors of the present invention vigorously pursued a study for accomplishing the above objects and, as a result, made the discovery that when an optical recording medium including a first recording layer containing Si as a primary component, a second recording layer containing Cu as a primary component and a dielectric layer provided adjacent to the first recording layer or the second recording layer was irradiated with a laser beam having a wavelength .lambda. via an objective lens having a numerical aperture NA satisfying .lambda. / NA.ltoreq.640 nm, Si contained in the first recording layer as a primary component and Cu contained in second recording layer as a primary component were mixed at a region irradiated with the laser beam, thereby forming a record mark whose reflection coefficient was different from those of other regions of the first recording layer and the second recording layer and a crystallized region whose reflection coefficient was different from those of other regions of the dielectric layer was formed at a region adjacent to the record mark, whereby the difference between the reflection coefficient of the region irradiated with the laser beam and those of other regions was increased as a whole, the C / N ratio of the reproduced signal could be improved and jitter of the reproduced signal could be lowered.

[0014] Therefore, the inventors of the present invention pursued a further study and, as a result, made the discovery that when an optical recording medium including a first recording layer containing one element selected from the group consisting of Ge, Sn, Mg, C, Al, Zn, In, Cu, Ti and Bi as a primary component, a second recording layer containing one element from the group consisting of Cu, Si, Al, Zn and Ag and different from the element contained in the first recording layer as a primary component and a dielectric layer provided adjacent to the first recording layer or the second recording layer is irradiated with a laser beam having a wavelength .lambda. via an objective lens having a numerical aperture NA satisfying .lambda. / NA.ltoreq.640 nm, the element contained in the first recording layer as a primary component and the element contained in the second recording layer as a primary component were mixed at a region irradiated with the laser beam, thereby forming a record mark whose reflection coefficient was different from those of other regions of the first recording layer and the second recording layer and a crystallized region whose reflection coefficient was different from those of other regions of the dielectric layer was formed at a region adjacent to the record mark, whereby the difference between the reflection coefficient of the region irradiated with the laser beam and those of other regions was increased as a whole, the C / N ratio of a reproduced signal could be improved and jitter of the reproduced signal could be lowered.

Problems solved by technology

However, since an organic dye is degraded when exposed to sunlight or the like, it is difficult to improve long-time storage reliability in the case where an organic dye is used as the material of the recording layer.

However, since the difference between the optical property of the record mark consisting of the eutectic formed of the elements contained in the two recording layers and those of other regions is not so large, it is difficult to record data in the optical recording medium only by forming a record mark of eutectic of elements contained in the two recording layers so that a reproduced signal having a good C / N ratio can be obtained.

In particular, in a next-generation type optical recording medium that offers improved recording density and has an extremely high data transfer rate, since the diameter of the laser beam spot used to record and reproduce data is required to be reduced to a very small size and the difference between the optical property of the record mark and those of other regions is required to be sufficiently large, it is extremely difficult to reproduce a signal having a good C / N ratio only by forming a record mark of eutectic of elements contained in the two recording layers.

The same problem occurs in optical recording media other than the optical recording medium constituted so as to form a record mark of eutectic of elements contained in the two recording layers.

Moreover, it becomes difficult to control the thickness of the first recording layer 31 and the second recording layer 32.

However, in the case where the difference in the reflection coefficient between the record mark M and other regions of the first recording layer 31 and the second recording layer 32 is not sufficiently large, a reproduced signal having a high C / N ratio cannot be obtained.

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